1. Field of the Invention
The present invention relates to disk drives for computer systems. More particularly, the present invention relates to a disk drive employing off-line verification and relocation of marginal sectors discovered during a read error recovery procedure.
2. Description of the Prior Art
Disk drives typically perform an error recovery procedure when a read error is encountered. The error recovery procedure typically involves performing a number of retry reads on the errant data sector while adjusting various parameters in the disk drive until the data sector is successfully recovered. U.S. Pat. No. 6,332,204 discloses a disk drive wherein a data sector is relocated if during a read operation the number of retries required to recover an errant data sector exceeds a predetermined threshold. However, the performance of the disk drive degrades as the number of relocated data sectors increases. In the aforementioned patent, a number of data sectors may be relocated unnecessarily if the read error is due to a bad write which may be overcome by rewriting the data sector rather than relocate the data sector. U.S. Pat. No. 6,233,108 discloses a disk drive which performs an off-line scan of all the data sectors by successively reading and writing data to each data sector on the disk. If a data sector requires multiple retries to recover, the data sector is rewritten and again read. If after rewriting a data sector it still requires multiple retries to successfully read, the data sector is relocated. However, verifying every data sector during an off-line scan is time consuming and inefficient since the number of defective sectors needing to be relocated is typically very small relative to the total number of data sectors.
There is, therefore, a need to improve the manner in which defective data sectors are located and relocated in a disk drive.